1. Field of Invention
This invention is directed to contact transfer of liquid immersion developed images. More particularly, this invention is directed to highly efficient contact transfer of liquid immersion developed images using a cohesive and/or adhesive overlayer over the developed image.
2. Description of Related Art
In order to enable contact transfer of a toner image from a first substrate to a second substrate the toner image must exhibit a higher adhesiveness to the second substrate than to the first substrate and the toner image must also be cohesive enough to prevent the toner image from breaking or separating during the transfer.
Toner images comprise a carrier liquid and toner particles. The toner particles typically contain pigments as well as other materials such as charge control agents. These materials are bound in a resin. Depending upon the qualities of the carrier liquid and the resin, the toner particles may be dissolved in the carrier liquid by varying degrees. If the resin particles are dissolved to such an extent that the toner particle boundaries are not well defined, then the cohesiveness of the toner image tends to be relatively high. Additionally, as the ratio of toner particles to carrier fluid increases the cohesiveness of the toner image also increases. The toner particles tend to combine or interact more with each other as the relative content of the toner particles increases.
Liquid immersion developed images have conventionally been transferred using electrostatic transfer or transfuse methods. Electrostatic transfer processes overcome the adhesiveness of the toner image to the first substrate by applying a voltage differential between the second substrate and the toner image. Typically, the voltage differential is on the order of 800 Volts. However, process control of electrostatic transfer is very narrow. In particular, solid content, developed mass per unit area, substrate range and other factors which affect the efficiency of the transfer are difficult to control. Additionally, transfer quality using electrostatic transfer is difficult to maintain.
Electrostatic transfer processes also often involve coating the paper with carrier fluid. The layer of carrier fluid smoothes the surface of the paper to prevent air becoming trapped beneath the toner image. However, it is very difficult to remove the carrier fluid from the paper. Electrostatic transfer without coating the paper with carrier fluid has been ineffective because of the breakdown of the voltages in the air that is trapped in the paper.
At ambient temperature, toners that are typically used for transfuse processes tend to have resin particles that have distinct boundaries and are not dissolved in the carrier fluid. Thus, the cohesiveness of the toner at ambient temperature is relatively low. Transfuse processes heat the toner image above the melting or solvating point of the resin particles. Above this temperature, the resin particles tend to dissolve into the carrier liquid and mix with adjacent resin particles and the cohesiveness of the toner is greatly increased.
While transfuse and/or transfixing processes result in a higher quality image than electrostatic transfer, because the transfuse process requires heat, many problems are encountered in controlling the effects of the heat. For example, registration is problematic because the dimensions of the components of a system vary due to the thermal expansions and contractions that result from heating and cooling the system components. Additionally, transfixing requires generating heat and controllably dissipating the heat, which requires additional processing time and/or elaborate heat transfer systems. Additionally, other processes may not be usable with a transfix method because these other processes may not react well to the heat.
Conventional systems for contact transfer of toner images require a substrate with a low surface energy. The low surface energy substrate does not adhere well to the toner image. Therefore, the toner image is relatively more adhesive to another substrate than to the first substrate. Examples of low surface energy substrates are described in U.S. Pat. Nos. 5,567,565, 5,576,818, and 5,585,905, each incorporated herein by reference in its entirety.
Low surface energy refers to a surface of a solid which has a low interfacial free energy between the image bearing member and the developed image. A low interfacial free energy means that the solid will not adhere well to the image. Therefore, it will be easier to transfer the image to a new substrate. The low surface energy provides an adhesion to a liquid immersion developed image that is weaker than the internal cohesion of the developed image and the adhesion of the developed image to another substrate.
Typical image developing systems have two transfers. In the first transfer, these systems rely upon a strong electrostatic transfer process to move the toner image from a first substrate with a high surface energy such as a photoreceptor body to a second substrate such as an intermediate image bearing member having a low surface energy. The intermediate image bearing member enables the use of an electrostatic transfer process because the high voltages do not adversely affect the intermediate image bearing member. Additionally, the intermediate image bearing member does not adversely affect the electrostatic transfer voltages like the recording paper described above.
Next, the toner image is transfixed from the intermediate image bearing member to a recording media such as paper. Because the intermediate image bearing member is a low surface energy substrate, the toner image adheres to the recording media better than it adheres to the intermediate image bearing member. Additionally, the toner image is cohesive enough to prevent separation of the toner image because the image has been transfixed through the application of heat.